One type of earth boring bits for drilling oil and gas wells has a bit body with at least one rolling cone, typically three. Each cone is mounted on a cylindrical bearing pin that depends downward and inward from a bit leg of the bit body. Annular thrust faces are formed on the bearing pin and in the cone cavity for reacting against downward thrust. The bearing pin thrust face is in a plane nominally perpendicular to an axis of the bearing pin. The cone thrust face is formed in a plane nominally perpendicular to the rotational axis of the cone. Initially, the thrust faces are parallel to each other. Lubricant is supplied from a lubricant reservoir to the spaces between the bearing pin and the cone.
While the bit is drilling, the thrust faces typically do not run precisely parallel to each other. The bearing pin deflects slightly because it is cantilevered from the bit leg. Also, because of tolerances between the cylindrical portions of the cone and the bearing pin, the cone can cock slightly relative to the bearing pin. This slight misalignment of the cone axis relative to the bearing pin axis results in a circumferentially converging-diverging space between the thrust faces, which can be beneficial because it can create hydrodynamic lubricant pressure between the thrust faces to help support the load. However, the bearing misalignment also concentrates thrust bearing contact loads, which is detrimental.